The present invention relates to a photointerrupter, and more particularly to a photointerrupter having a novel terminal arrangement.
In a conventional photointerrupter, a light emitting portion and a light detecting portion are prepared separately and then assembled into a unit package such that they are spaced one from the other and coupled with respect to radiation created and detected thereby, by an air gap region. However, such a conventional photointerrupter makes it difficult to ensure an alignment of optical axes of the light emitting portion and the light detecting portion, and in addition the assembling work is complicated.
To this end, an improved structure is illustrated, for example, in Japanese Laid-Open Patent Application No. 88876/1984 dated May 22, 1984, wherein a semiconductor light emitting element (an emitter pellet) and a semiconductor light detecting element (a detector pellet) are mounted on a lead frame and resin-sealed in common to form a resin molded single package. As shown in FIG. 1A and FIG. 1B, an emitter portion 12, a detector portion 14 and a bridge portion 16 are formed commonly by a transfer molding using a two-split metal mold. Emitter leads 22 and detector leads 24 are derived from opposite side surfaces of the resin-molded package. The emitter leads 22 are bent rectangularly at a portion where a emitter pellet 32 is mounted so as to be in face-to-face relationship with the detector portion 14. Similarly, the detector leads 24 are bent rectangularly at a portion where a detector pellet 34 is mounted so as to be in face-to-face relationship with the emitter portion 14. Then, a construction is such that the emitter pellet 32 and the detector pellet 34 mounted each in opposite mounting areas of both the leads are photocoupled through each convex lens 18. In the example, the bridge portion 16 must have an opening at the center for simultaneous formation of the lenses 18 by means of a two-split metal mold, and a width L of the opening should be formed greater than a diameter D of the each lens 18.
While the photointerrupter with the aforementioned structure attains a resin-molded single package with convex lenses by using a two-split metal mold, the following problems still remain unsolved.
The emitter pellet and the detector pellet are mounted on the common lead frame, and after a predetermined wire bonding is carried out thereon, the lead frame must be bent rectangularly so as to make each mounting area in a face-to-face relationship, however, if it is bent after mounting, the bending strain is capable of exerting an influence on the pellet mounting areas, thus deteriorating a reliability of bonding strength and pellet function. It would be conceivable that the lead frame be bent before mounting. However, the emitter lead frame and the detector lead frame must be separated in such a case, how to mate both the two may be problematical incidentally, and further processes for mounting and wire bonding become intricate in addition, and hence the method is unadvisable.
Further, all leads must be bent again in the same direction like a dual in-line package of the type commonly employed for housing semiconductor devices. However, since the bending process follows the resin-molding process, a bend is provided at a predetermined position spaced apart from a derived end portion so as not to cause a crack on the resin part. Therefore the photointerrupter may inevitably be of considerable dimensions in the direction of optical axis.
Moreover, since the opening is in enevitably at the bridge portion for forming the convex lenses simultaneously at the molding process, mechanical strength of the bridge portion becomes weak. For reinforcement, the photointerrupter must be increased in dimensions perpendicular to the optical axis.
As described, the structure of the resin-molded photointerrupter package proposed by the prior art has not yet been commercialized particularly for intricateness of the manufacturing process, and in addition the product itself gets inevitably large-sized.